Pressure transfer reproduction

ABSTRACT

IN PRESSURE TRANSFER PRINTING A PRINTED SUBSTRATE PATTERN ON A BASE MEMBER CONFERS DIFFERENCES IN THE BOND STRENGTH OF A SUBSEQUENT PIGMENTED TRANSFER COATING IN RELATION TO THE BASE MEMBER WHEREBY THE EDGE DEFINITION OF CHARACTERS PRINTED BY CONTACT PRESSURE WITH SAID PIGMENTED COATING IS DEFINED BY THE PATTERN OF THE PRINTED SUBSTRATE COATING.

y 0, 1972 R. J. WRIGHT 3,666,524

PRES SURE TRANSFER REPRODUCTON Filed Sept. 4., 1970 United States Patent 3,666,524 PRESSURE TRANSFER REPRODUCTION Robert J. Wright, Tranmere, South Australia, Australia, assignor to Research Laboratories of Australia Pty. Limited, Eastwood, South Australia, Australia Filed Sept. 4, 1970, Ser. No. 69,561 Int. Cl. B41m 5/10 US. Cl. 117-36.4 5 Claims ABSTRACT OF THE DISCLOSURE In pressure transfer printing a printed substrate pattern on a base member confers differences in the bond strength of a subsequent pigmented transfer coating in relation to the base member whereby the edge definition of characters printed by contact pressure with said pigmented coating is defined by the pattern of the printed substrate coating.

This invention refers to manifolding and in particular refers to a method and means whereby the image definition may be improved, particularly in one time multicopy pressure transfer information reproduction processes.

It is a known requirement in many varied situations for copies of information to be required, and common for such multiple copies to be required to be produced simultaneously. It is well known, for example, to produce multiple copies simultaneously using a typewriter or a computer print-out device or the like. Such simultaneous copy production is carried out by arranging for the sheets upon which the information is to be recorded to be placed in contact with a layer of a pigmented or otherwise coloured composition, such sheets being arranged in a stack containing suflicient sheets to produce the required number of copies. The stack is positioned on a suitable backing member and a type face of the required letter or character is contacted with the opposite side of the stack. Transfer pressure is applied by the introduction of relative motion between the backing and the type face, either the backing or the type face being moved towards the other to produce a sharp impact.

A disadvantage of the above described process results from the geometry of impact. The raised type face forms a relatively sharp impression on the two or three sheets closest to that side of the stack adjacent to the type face, with the edge delineation of the impression becoming successively less sharp as the impression passes through the stack towards the backing member. This feature is brought about to a large extend by the relatively planar nature of the backing, which accentuates the diffusion. of the impact forces as the sheet become progressively further removed from the type face. The normal impact forces may also be further diffused by the characteristics of the paper and tissue being used for manifolding, but even When specially selected papers and tissues are employed, readability requirements normally allows the production of a maximum of about copies, particularly with the computer printout devices in common use.

A further feature of this impact spreading effect is the reduction in the normal impact force or pressure that accompanies the loss of edge sharpness. This reduces transfer efficiency and makes it necessary for the carbon tissue or other colour transfer medium to contain on its surface a heavier or thicker deposit of colouring matter than would be required if complete facsimile transfer could be obtained throughout the stack. This increases the cost of the tissue to a figure considerably higher than would be necessary if a more efficient transfer system could be used. The carbon tissue can be produced to allow easier release under transfer pressure, but such tissue is "ice very difficult to handle because of the relative ease with which the pigment deposit is removed from its backing.

This present invention teaches a method whereby the adverse effects of the transfer geometry may be minimised, and in addition this invention provides a carbon or other transfer tissue with improved but controlled release properties, which improved release properties still allow the tissue to be handled without excessive offsetting of carbon from the tissue to other objects in contact with the coated surface.

In accordance with this present invention a tissue or other surface is prepared for carbon coating by first coating the surface in pattern form with a substrate material which has a different affinity for the carbon coating than that of the original surface. Such substrate material is coated by any known means, such as screen printing, letterpress printing, flexography or the like, and is coated in pattern form, such as by the use of a 50% dot area pattern of 150 lines per inch screen size. We have found resolution improvement to be attained with screen patterns as coarse as lines/ inch, and while a screen finer than line may be used with beneficial effect if required, for most purposes the 150 line screen will be found to be sufficiently fine. In addition the pattern as printed need not necessarily be a 50% dot pattern, but should preferably be such that the areas from which carbon release is ultimately to be obtained is in the form of disconnected uniform dots, which can be square, round, or rounded. Thus in those instances when the patterned material allows easier release of the colouring layer the patterned material should be discontinuous, whereas in those instances in which the patterned material does not release the colouring material as readily as the backing, the pattern should be continuous, with disconnected areas of the previously described preferred shape included as uncoated areas within the pattern.

The carbon coating is applied as a uniform layer overlying the printed or otherwise produced substrate pattern, and thus has release properties which vary in pattern form. When such a carbon coated sheet is used for pressure transfer printing the release of carbon is largely confined to those areas in which the bond between the carbon coating and the backing is least. When such a carbon tis sue is used for pressure transfer printing the controlled release allows the production of relatively sharper edged copy than would be produced without our novel substrate, as the release pattern in effect produces substantially uniform fracture lines in the carbon coating when pressure is applied. Provided the screen pattern is of sufficient fineness the edge delineation of the pressure transfer image will be quite sharply defined, and thus the screen pattern should preferably be at least as fine as 100 lines/inch.

As a further advantage this present invention allows the carbon coating to be formulated to provide complete release in those areas where release is desired under moderate pressures without introducing mechanical handling problems, as the areas in which release is not required effectively increase the smudge resistance of the carbon deposit. Consequently it is also possible when using this present invention to reduce the weight of the carbon deposit on the tissue and still obtain clearly defined pressure transfer images of acceptable density.

A further feature of this present invention is the possibility of printing in pattern form on the base sheet a substrate material which either assists carbon release or inhibits carbon release as desired. This widens the choice of base sheets usable for instance for reverse carbon pressure tranfer application, in that a sheet with poor carbon release properties may have coated thereon in patterned form a substrate material with enhanced carbon release properties, while a material possessing carbon release properties which would cause it to be diflicult to handle can have a release inhibitor applied in pattern form prior to carbon coating, thus allowing advantage to be taken of the good carbon release properties of such a base without introducing handling difliculties.

In order that the invention may be more fully understood reference will now be made to the drawings in which FIG. 1 is a cross section of a tissue in accordance with the present invention produced using conventional coating techniques, whereas FIG. 2 is a cross section of a tissue produced in accordance with the present invention with the pigmented pressure transferable coating coated on the substrate bearing base using electrostatic coating techniques.

Referring to FIG. 1 in more detail, a paper base 1 has coated on one side a patterned coating 2 of a material whose release characteristics in relation to the subsequently applied pigmented pressure transferable coating 3 are diiferent from those of the paper base 1.

In FIG. 2 it is shown that the presence of a patterned substrate 2 with higher electrical resistivity than that of the backing paper inhibits electrostatic deposition in those areas, resulting in the pigmented pressure transferable coating being of greater thickness in those areas of the base member 1 not covered by the patterned substrate coating 2.

The transfer mechanism of the invention is illustrated in FIG. 3, in which 4 represents a sheet of paper on which an image is to be printed using pressure transfer methods and the curved line 5 represents the irregular pressure the tissue of the present invention allows the production of sharp edges on the printed image, as shown in the image deposit 6.

We have also found it advantageous although not necessary to apply the carbon coating under the influence of an electrostatic field. This allows the production of a carbon coating in which the shear strength of the coating normal to the base is less than the bond strength between the base and the carbon layer, and also allows the deposition of carbon on those areas from which transfer is not to take place to be less than on those areas from which transfer deposition is to take place particularly if the substrate material has been so selected that the electrical conductivity of the areas from which carbon transfer is to be effected is difierent from that of those areas from which no transfer is to take place. These features in combination still further increase the edge sharpness of the pressure transferred image and reduce carbon wastage by restricting the amount deposited on those areas from which transfer is not required.

Various substrate materials with carbon release properties different from those of the paper or other backing material have been found to be usable in accordance with the principles of this invention. These materials have been coated to form a substrate in pattern form on various backings and then overcoated with a carbon pressure release composition. It should be understood that the term carbon pressure release composition is intended in the generic sense and that the term carbon paper is in common usage even when the actual pressure release coating does not contain carbon as a colouring material.

Materials which we have applied in pattern form to various paper stocks which have a greater affinity for the carbon coating than that of the uncoated paper have included cellulosic resins, vinyl-acrylic emulsions, silicones and the like, whereas materials which have provided areas of lower bond strength than the uncoated stock have included molybdenum sulfide, polytetrafluoroethylene, fiuorinated ethylene-propylene, and the like. These materials have been coated in pattern form on various bases, such as onion skin, bond paper, bank paper, electrophotographic base paper, clay coated stock and the like. The patterned coatings have been applied by letterpress printing methods, stencil printing methods, screen process printing and the like.

The carbon coatings have been applied to the patterned release side of the base stock by brushing, spraying, cold and hot roller coating and the like, and in addition electrophoretic coating methods have been used with the advantages as previously described. The carbon coatings used have generally been of the well known type containing pigment, synthetic or natural wax, petroleum jelly, non-drying oils, non-drying synthetic resins and the like. Advantageously polarity control agents are also included when the carbon coating is required to be produced by electrophoretic deposition methods.

It will be appreciated that the formulation of the carbon coating may be varied to give greater or less adhesion to the paper backing, and to possess varying degrees of smudge resistance. Such formulation variation will affect the choice of patterned release agent applied as substrate prior to carbon coating, and in fact some of the materials already referred to as providing bond strength greater than that of the paper may actually olfer easier release than the paper when used in conjunction with particular carbon coating compositions.

In order tofurther illustrate this invention, reference will be made to the following examples. However, these examples should be read in the illustrative sense only as one skilled in the production of pressure release coatings will be able to adapt other formulations and materials to the present invention without departing from the scope of the invention.

EXAMPLE 1 Grams Parafiin wax 64 Spindle oil 56 Petroleum jelly 26 Victoria blue, C.I.' Pigment Blue 2 40 Carbon black 14 Odourless mineral spirits 200 The odourless mineral spirits was a substantially aliphatic hydrocarbon solvent, flash point F., KB value 26, Sp. Gr. 0.761, aniline point 35 C., marketed by Sheel Co. under the trade name Shellsol T.

The components were charged into a ball mill and milled for 24 hours, after which the mixture was coated on the substrated sheet of manifold paper using a number 20 wire wound rod to produce a coating with a dry weight of 5 grams/sq. meter. The carbon pressure release coatmg was allowed to dry and the thus produced tissue sheet cut to provide sufiicient tissues for a ten sheet manifold set, which was imaged in a typewriter. Due to the presence of the patterned substrate coating, the tenth copy was of adequate definition to be classed as usable, whereas the same carbon pressure transfer coating coated on the same manifold paper without the patterned substrate did not produce a readable tenth copy.

EXAMPLE 2 The cellulose resin used as a substrate in Example 1 was replaced with a vinyl acrylic resin emulsion. The vinyl acrylic resin used was a vinyl acetate acrylic copolymer, pH 4-5, viscosity 3000-4000 cp., specific gravity 1.10, solids content 55%, supplied by Polymer Corporation under the trade name Acropol CA103.

EXAMPLE 3 The cellulose resin substrate of Example 1 was replaced with a silicone resin. The resin used was Dow Corning 805 resin, Sp. Gr. 1.01, viscosity 80-150 cp., supplied as a 50% solution in xylene.

EXAMPLES 4-6 The manifold paper backing of each of Examples 1-3 Wts replaced with 11 /2 lb. Finch Pruyn Multiform paper, a tissue produced specifically for use in conjunction with pressure transferable carbon coatings.

EXAMPLES 7-12 In each of Examples 4-6 the carbon coating was replaced with the following:

The Odourless mineral spirits, zirconium octoate, carbon black and Victoria blue were mixed together to absorb the zirconium octoate to the pigments, after which the remaining components were added and the mixture milled in a ball mill for 24 hours.

The coating composition was further diluted with odourless mineral spirits in the proportion 1-10 grams coating composition to 100 grams odourless mineral spirits and placed in an insulating container. The substrate coated backing member was placed on a plate electrode with the coated side remote from the electrode and placed in the container with the sheet facing another electrode and spaced 1" apart from such electrode. The electrode containing the sheet to be coated was connected to the negative output of a high voltage supply and the other electrode was connected to the positive output of the same supply, which positive output was in addition grounded. Application of 15 kv. for a period of 10 seconds produced a carbon coating on the paper, such coating having an average weight of 4 grams/square meter. However, the coat ing in those areas not covered by the substrate was substantially heavier than in the substrate covered areas, and thus was of adequate thickness for use as a pressure transfer coating in the areas of maximum release, and substantially thinner in areas from which release was not required.

In each of Examples 1 through 12 the substrate coating was such that it retarded release of the pressure transfer coating to a greater extent than the uncoated areas of the backing member.

EXAMPLE 13 The substrate coating of Example 1 was replaced with polytetrafiuoroethylene. The polytetrafiuoroethylene was in the form of a dispersion in a fluorocarbon propellant, and was sprayed on to the manifold paper through a 100 mesh silk screen.

6 EXAMPLE 14 The polytetrafluoroethylene of Example 13 was replaced with fluorinated ethylene propylene.

EXAMPLE 15 The polytetrafiuoroethylene of Example 13 was replaced with a similar suspension of molybdenum sulfide.

Generally we have found the thickness of the substrate coatings to be relatively non-critical, and have used coating weights equivalent to uniform coatings ranging from 1 to 4 grams/sq. meter without any significant difference in effectiveness.

It will be seen that the present invention offers a means of improving the definition of pressure release printed images by provision of a novel base sheet for carbon coating, which base sheet has controlled carbon release characteristics in pattern form.

What I claim is:

1. An improved tissue for pressure transfer printing consisting essentially of a base member having coated thereon in dot patterned form a substrate layer and having as a further coating a pressure transferable pigmented layer, characterised by such substrate layer being present only in areas defined by said pattern whereby the pressure transferability of said pigmented pressure transfer? able layer varies in accordance with said pattern.

2. An improved tissue for pressure transfer printing in accordance with claim 1 in which the pressure transferable pigmented layer is bonded more firmly to the substrate coating than to those areas of the backing not covered by the substrate.

3. An improved tissue for pressure transfer printing in accordance with claim 1 in which the pressure transferable pigmented layer is bonded more firmly to the backing than to the substrate coating material.

4. An improved tissue for pressure transfer printing in accordance with claim 2 in which the patterned substrate consists of a continuous pattern of a material taken from the group cellulosic resins, vinyl acrylic'resins, and silicone resins, the pattern of substrate deposition being in the form of a 50% dot pattern of fineness varying between and lines per inch in each direction.

5. An improved tissue for pressure transfer printing in accordance with claim 3 in which the patterned substrate consists of a pattern of disconnected dots of a material taken from the group molybdenum sulfide, polytetrafluoroethylene and fiuorinated ethylene propylene, said disconnected dots being in a patterned form of fineness varying between 100 and 150 lines per inch in each direction.

References Cited UNITED STATES PATENTS 3,531,312 9/1970 Newman 117--36.4 3,340,086 9/ 1967 Groak 117-364 3,099,571 7/1963 Maierson et al 11736.1

MURRAY KATZ, Primary Examiner US. Cl. X.R. 

